Paint Shop Pro :: X5 SP2 Corrupts Big TIFF Files At Save Time

I wanted to upgrade from paintshop pro x2 to x5 (want to go to 64 bit)but I have a severe problem. Here the steps to reproduce it:

1. open only one big tif file at a time (edit window) (from canon scanner 600 dpi A4 scan around 100 mb per file i think around 5500 to 3200 pixels)

2. sometimes i turn/rotate the picture first with the rotate tool (0 to 0,2 degrees)

3. use the crop/trim function to cut a small part of the edge

4. save the image and close it ( there is never more than one file opened in psp) its now around 80 mb in size dont close psp x5 and repeat steps 1 to 4 with other images. (with smaller 30mb images it did not happen and if I close x5 and reopen it after every 5th tif-image it does not happen too, so somewhere memory is not given free) When doing this when saving somewhere at the 7th - latest at the 10th image that image is saved corrupted.(it shows in the lower half vertical grey lines)

The big problem is: there is no error message and you only see that the image is corrupted when you view it again or if you see it in the thumbnail view of windows explorer.

second problem is that after doing an undo after a crop/trim step (3.) the picture is gone and the area is white.(dont save now!!)

x5 version is the current trial version (15.2 something - when i try to install sp2 it says its not necessary)

this happens on 2 different machines

mach 1: intel nuc i3217u 8GB ram, c drive 128 gb ssd, pic-drive: usb hd with 500 GB

mach 2: i7 2600k, 16 gb ram, cdrive 128 gb ssd, pic drivé: internal 2tb hd or internal ssd 256 gb (makes no difference)on both machines psp x5 system info only shows 4GB ram free so it seems its not really 64 bit programm.