You probably have the "Always on Top" option checked (under the Options menu)
It is a feature not a bug.
Always on Top
Click on the Options Menu, then click Always on Top to
cause IrfanView to always be visible on your screen,
even when you open other programs. This can be removed
at any time by clicking Always on Top again.
Anti-wrinkle cream there may be, but anti-b astard cream there is not..