FS#34066  describes the effect this bug has on devtools. But the underlying bug is with pacman so this task is more appropriate.

Set IgnorePkg=foo and run pacman -Sp foo. Instead of seeing the URL for the package foo as stored on the highest priority mirror, you will see an empty string. This is a bug since documentation says --ignore will only take effect on a sysupgrade operation not a print.

Moreover, this behaviour is confusing since it is the opposite of what --noconfirm would do. The options --noconfirm and --print are both supposed to surpress questions. However the question "Foo is in IgnorePkg/IgnoreGrp install anyway?" defaults to "yes" with --noconfirm meaning that pacman will continue the operation and install the package. However, the same question defaults to "no" with --print meaning that pacman stops what it is doing and returns.

The reason for this in the code is fairly clear. The question_cb function returns without a value whenever config->print is TRUE, leaving the value at the mercy of libalpm. It should really return predictable default values similar to how config->noconfirm would.