[pp. 211] Very often...the verb of the cum clause is in the subjunctive mood, especially when it describes either the general circumstances (rather than the exact time) when the main action occurred (often called a "cum circumstantial clause")
The example used is cum hoc fecisset, ad te fugit, which is obviously pluperfect subjunctive.
M&F, on the other hand, states:
[pp. 287] If the cum clause states the circumstances in which the action of the main verb takes place, it is called a circumstantial cum clause...When the action in such cum clauses refers to present or future time, the indicative is used...[When the action] is in the past time, the subjunctive is used
The examples given are cum te videbo, felix ero and cum te viderem, felix eram, which are future indicative and imperfect subjunctive, respectively.
Is Wheelock's ignoring circumstantial cum clauses in the primary tenses, or am I missing something?