Are canister custodians able to upgrade canister code?

@Severin We tried to get a canister to upgrade itself (more details on the other topic) with some very mixed results. On one hand, the call failed and the execution stopped after the install_code call to the management canister but on the other hand the upgrade went through successfully.

We speculate that it’s because the underlying wasm is changed but it’s still perplexing what is happening exatcly.