Thanks for the reply Mathias.  I am using b2282 - that is the most recent isn't it?
The 
selection bug-this is difficult to explain, it had occurred a while back and then in a recent release what I believed it to be was listed in the list of fixes & the problem 99% went away. I now cannot find the update list which included this 
fixed description.   

Basically if you selected one or more files within a group and then moved/copied them to the opposite pane, selecting another block of files would often start from a random point in the collection of files.  This happened between dirs on the same physical disk+partition. (Maybe this is related to the delay in the 'grab focus thing?  All my disks say 100% okay & the FATs etc pass windows checkdisk tho...)
The focus of the last highlighted file would somehow randomly move so that a select+shift could start in a random location and a random selection of files would be highlighted for the next operation.  I suspected that the mouse cursor + overlay was involved. Difficult to explain it without videoing it.  It did occur once yesterday on a directory with a hundred files present.
E.g. 
I select 10 files from a folder holding 100 files, I move these 10 files to the opposite pane;
I have highlighted another file as the copying operation occurs, I press shift and select the last file hi-lighting a new block;
the highlight grabs a random block which ends with my end selection click. 
So the hi-lite selection grabs extra/different files
1
2-hi-lite
3-hi-lite
4-click
5-shift
6-shift
7-shift
8-shift
9-shift
10-shift+click - hi-lite
11
12
13
14
15
16
This could be really crazy sometimes adding dozens of extra files to the next operation.  Sometimes the selection would extend into off-screen area that could only be seen by using the scroll bar.  It wasn't really frequent & I couldn't decide how to describe it ....  then you seemed to fix it.
But maybe you meant something different & my PC is just trying to make my head explode... 
 Grab focus
Grab focus-normally whilst the copy or move operation occurs I can select something else and begin or queue another operation from another dir.  Moving out of the current dir, whilst the initial op commences, now delays. 
I must wait and MC will enter a 'not responding' state if I click 'up' to move up the tree, whilst it begins the copy or move operation. 
I had wondered if this was due to the USB drives that I copied some items to but these are USB 3.0 drives on the USB 3.0 socket & it also happens between SATA hard disks within the system.
So I mean it is grabbing focus as it starts a function and this is preventing me from clicking on/doing anything else.
I have been resetting 
column width and then setting as default. But I maybe hadn't clicked 
save as default since installing the last beta ...I thought I had!  
I have now it seems to be okay!
OK on the 
Find switch/functionalities, I can wait  & use regex etc so it's not life-threatening (yet!)