There are two recently available patches to NET+OS V7.5 that collectively address this issue.
Firstly, I want to assure you that I replicated the issue you described BEFORE installing these patches. Then I installed these patches and reran pbuilder. After the patches, pbuilder worked cleanly.
This will bring your installation up to the latest and greatest
A couple of caveats
1) netos750_to_752_sp is huge. It brings NET+OS up to the latest meaning that most/all libraries re replaced. So this takes a while
2) Before starting the package manager-related update ensure the following:
a) That the API reference guide is CLOSED
b) That any pdf or other documentation components are closed
c) That any editable files are closed. You might be advised to close your editor, just in case.
ESP replaces files, so any files that it needs to replace that are open, will cause the installation to fail.
3) If while installing package manager appears to hang, right click on the window. A subwindow that was subsumed, may pop to the front. It may be looking for input.
As I stated my findings are such that these updates should put you on the right track.
As with any major update, you might want to back up your installation tree before performing the package manager update (just to be safe).