[ubuntu_mate] File checksums "temporarily" wrong?

I'll preface this post by saying that I'm a layman when it comes to security in general and cryptography in particular, so please forgive me if anything that follows comes off as particularly uninformed.

I am using a fresh (installed yesterday) copy of 16.04 MATE and verified the MD5, SHA1 and SHA256 hashes of the disc image multiple times before buing. I downloaded the image again onto a shared partition when the install was complete in order to start a new VM, and everything seemed to check out when I checked the image's sums again.

Something strange happened during and after the install itself, though. I checked the sums again as the VM was installing and found that the SHA1 and SHA256 sums of the file had changed; ruing it again all three of the sums were different. I was conceed by this and continued to check the sums to see if they changed again- and they did, back to what they were supposed to be. Later in the day they seem to have changed yet again though, even after the VM was closed, before retuing to their originals (as they seem to be right now).

My question is: should I be conceed about the fact that these hash functions periodically retued incorrect sums, and could this indicate that something on my system is maliciously modifying files in some way? I tend to be paranoid about this sort of thing and I'm pretty sure I must be overreacting to something iocuous, but I would like to defer to someone with more expertise on these things in any case.

FWIW debsums -c retus the following on this and my other 16.04 installs:

/boot/vmlinuz-4.4.0-21-generic
/usr/lib/python3/dist-packages/cupshelpers/__pycache__/__init__.cpython-35.pyc
/usr/lib/python3/dist-packages/cupshelpers/__pycache__/config.cpython-35.pyc
/usr/lib/python3/dist-packages/cupshelpers/__pycache__/cupshelpers.cpython-35.pyc
/usr/lib/python3/dist-packages/cupshelpers/__pycache__/installdriver.cpython-35.pyc
/usr/lib/python3/dist-packages/cupshelpers/__pycache__/openprinting.cpython-35.pyc
/usr/lib/python3/dist-packages/cupshelpers/__pycache__/ppds.cpython-35.pyc
/usr/lib/python3/dist-packages/cupshelpers/__pycache__/xmldriverprefs.cpython-35.pyc