This issue was first reported in v7.62 here
in relation to remote desktop.
As I said in that thread, I couldn't see anything that changed from v7.61 to v7.62 that would cause the issue, and perhaps the issue was present before that.
If you run mIRC v7.61, 7.62, 7.63, etc. can you reproduce the issue? How about with earlier versions? Is there a version where it definitely starts for you?
But, as I said, if you are seeing this issue when Photoshop is being run, and photoshop is using up available memory/resources, practically anything can and will happen.
If previous users reporting this issue are also seeing it due to lack of available memory/resources/etc. then we know what the cause is and there is nothing that can be done.
If previous users are not seeing this due to lack of memory/resources, the cause is something else.